a) Field of the Invention
This invention relates to an apparatus for locating objects within a body, and particularly concretions situated in body cavities, in three dimensions, and for destroying them, comprising an electro-acoustic treatment transducer for generating shock waves for treatment purposes to be emitted to focus on the object concerned and at least one B-scanner connected to the treatment transducer to act as a locating transducer for locating the object, the locating transducer being adjustable relative to the treatment transducer along a preset path at a constant distance from the shock wave focus (co-focally therewith) so that, depending on the position of the locating transducer, B-scan images can be generated and displayed in different cross-sectional planes and from different viewing angles.
b) Description of the Prior Art
Ultrasonic locating systems employing B-scanners in known apparatus of the present kind (lithotripters) still do not provide the doctor with sufficient information on the size, volume and surface of the concretion to be treated. However, particularly when large gallstones are being treated, it is most important for a satisfactory assessment to be made of the shape and dimensions of the stone, including while the treatment is going on, firstly because an attempt must be made to disintegrate the stone to the maximum possible degree and secondly because there needs to be some way of obtaining exact information on the success achieved with the treatment at the time from the B-scan images shown on a monitor and of documenting this success where required.
It is known (DE 35 43 867 (U.S. Pat. No. 4,832,730) FIGS. 1 and 2) for the locating transducer and the treatment transducer to be arranged on the same axis and for the locating transducer to be adjustable relative to the treatment transducer in rotation on this axis and axially along it. It is true that this allows B-scan images to be generated in various cross-sectional planes, but the concretion cannot be looked at from different viewing angles, hence this solution is still not ideal as far as the information content of the B-scan image is concerned.
A better solution in this respect is one (DE 3543867 C2, (U.S. Pat. No. 4,821,730) FIGS. 3 and 4) in which the locating transducer is externally positioned at the circumference of the treatment transducer and can be adjusted on a circular path concentric with the longitudinal axis of the latter transducer, because when this is the case the concretion intended for destruction can be imaged and studied from different viewing angles as dictated by the position of the locating transducer.
However, even this solution has certain drawbacks relating to accuracy of aim because the sound fields of the two transducers do not travel the same distance through the same media and hence it is not always possible to be sure that the cross-hairs which identify the position of the shock wave focus in the B-scan image, and which may for example be marked on the screen of the monitor belonging to the locating system, do in fact show the correct position of the focus relative to the concretion seen in the image.
Also, it is not possible with the embodiment being discussed for the B-scanner to be arranged at an ideal angle to the axis of the treatment transducer. This is because the angle in question is too large, due to the locating transducer being positioned on the outside of the treatment transducer, thus making it difficult or even impossible, for structural and anatomical reasons, for the sector-shaped scanning plane of the locating transducer to be lined up on the concretion.
Hence it is better for one or more locating transducers trained on the shock wave focus to be arranged on or in the treatment transducer at an acute angle of, for example 15.degree. to the longitudinal axis of the latter (DE 27 22 252 C3; "Piezolith 2300" brochure, issued in September, 1988 by Richard Wolf GmbH, D-7134 Knittlingen, West Germany). However, the solutions of this kind known to date once again suffer from the drawback that the concretion cannot be displayed and studied from different viewing angles.
Hence, the main object of the present invention is substantially to improve the dynamic characteristics, and thus the information content, of the B-scan image generated by the locating transducer or transducers in comparison with known solutions.